A large number of RNAs are not diffusely distributed in the cytoplasm, but are actively transported to various subcellular sites. After reaching their final destinations, localized RNAs are translated, thus directing local protein production. While increasing numbers of localized RNAs are being identified, the functional importance of these events is not well understood. We are focusing on a localization pathway that we have identified, which targets a number of RNAs to cellular protrusions. This pathway is of interest because it targets RNAs encoding factors that have been implicated in progression of various types of cancers. Furthermore, as we have found, it is regulated by APC (Adenomatous Polyposis Coli) a tumor-suppressor protein, whose loss underlies the initiation of most colorectal tumors, as well as by the RNA-binding protein FUS, a protein mutated in cases of Amyotrophic Lateral Sclerosis. One aspect of our work focuses on understanding the molecular mechanisms underlying localization of RNAs at protrusions, and the consequences of localized translation on the function of the encoded proteins. We have revealed that localization of APC-dependent RNAs relies on a subset of modified, detyrosinated microtubules, providing, to our knowledge, the first evidence of any microtubule modification controlling RNA localization. Furthermore, we have made the intriguing observation that the mechanical properties of the extracellular environment influence the localization of APC-dependent RNAs. Specifically, increased substrate stiffness promotes actomyosin contractility, which in turn enhances formation detyrosinated microtubules thus promoting localization of RNAs at protrusions. Given that the stiffness of the extracellular environment promotes various aspects of metastatic behavior, we are currently testing whether the mechanism we have uncovered is involved in promoting migration of metastatic cells. Towards this goal we have devised ways to disrupt localization of APC-dependent RNAs either as a group or individually and assess the consequences on 2-dimensional or 3-dimensional model systems. Indeed, these approaches are revealing that localization of APC-dependent RNAs at protrusions is important for efficient cell migration and that disrupting the localization of just one of them is sufficient to cause significant defects. We are optimizing our current approaches for in vivo delivery to further test the roles of APC-dependent localized RNAs in animal models of tumor metastasis. Apart from migrating cells, our recent studies have revealed that APC-dependent RNAs are also localized in non-invasive, epithelial cells, where they are concentrated at the basal surface. A separate line of investigation is thus exploring the functional roles of basally localized APC-dependent RNAs in 2D or 3D epithelial systems. Given the role of APC as an initiator of tumorigenesis in the intestinal epithelium, we believe these studies might reveal roles of localized RNAs relevant to the initial stages of tumor formation.